Tornillo literally means "screw". It's a fantastic word to learn from this song because it's used in a very common Spanish idiom and is also the artist's name!
In the song, he sings, "Me hace falta un tornillo", a playful expression that literally means "I'm missing a screw". It's the Spanish equivalent of saying "I have a screw loose" or "I'm a little crazy", and he uses it to proudly embrace his wild side. It's an especially clever line, as it's a nod to his own stage name, Tornillo.
Tornillo blends hip hop beats with cumbia flavor in "Morena", an ode to a girl who caught his eye at a neighborhood party and vanished. Ever since he saw her dance, he cannot get her red lips and long hair out of his head: "Bailando la cumbia se ve bien buena / Pelo largo, boca que quema" (Dancing cumbia she looks so fine / Long hair, a burning mouth). He met her in the barrio (neighborhood), but now she is nowhere to be found, leaving him asking where to go just to see her again. People on the corner warn him that she is trouble, whispering "que eres una criminal" (that you are a criminal), yet he brushes the rumors off because he is too hooked to care.
Between trying to track down his crush, Tornillo puts his roots front and center. He shouts out his home turf in San Luis Potosí, specifically the streets of Cactus ("Puro Cactus, perros" / Pure Cactus, dogs/homies). He jokes about his own reputation too, embracing the chatter that smoking too much weed has him losing his mind: "Me hace falta un tornillo y nunca lo voy a cambiar" (I'm missing a screw and I'm never going to change it). It is a clever, cheeky nod to his own rap moniker, Tornillo ("Screw"), tying his neighborhood pride and love of street life straight into his infatuation.